1. Field of Invention
The present invention relates to the field of safety inspection technology, in particular to an ion mobility spectrometer for inspecting drugs and explosives by means of ion mobility technique as well as an ion storage and extraction method applied to the ion mobility spectrometer.
2. Description of Prior Art
Ion mobility spectrometer discriminates different ions according to the fact that different ions have different drift velocities in a uniform weak electric field. The ion mobility spectrometer is usually formed of a sample input section, an ionization section, an ion gate, a drift region, a collection zone, a sensing circuit, a data acquisition and processing and control section, etc. In the prior art, Bradbury and Nielson gate is used to provide ions generated during the gate-opening phase to the drift region. Those ions generated during the gate-closing phase are scattered onto the tube wall by the ion gate and thus wasted without being stored.
CN Patent No. 200310106393.6 discloses an ion storage method, in which three pieces of mesh electrodes takes place of Bradbury and Nielson gate to form a storage region, and ions are stored in a non-electric field zone between the first two pieces of electrodes during the ion storage phase. When the ions are to be driven into the drift region for ion migration, the first piece of mesh electrode is changed to drive the ions into the space between the second and third pieces of mesh electrodes. Then, the second piece of mesh electrode is changed to drive the ions into the drift region for further migration and discrimination. Here, the stored ions have to pass through the mesh electrodes twice, and thus bumping and scattering will affect sensitivity. In additional, this process requires very complex control.
U.S. Pat. No. 5,200,614 also describes an ion storage method, in which sensitivity will be affected due to the problem of compounding between positive and negative ions at the ion storage phase. In this method, although the configuration is simplified by integrating the ionization zone and the storage region, some constraint is posed on the size and shape of the ion source, causing trouble in further application.
Both of the above solutions require a long gate-opening period to provide the ions into the drift region. This will cause spread in mobility spectrum peak shape and affect resolution for the same drift region.